Prostaglandins in the zebrafish ovary: Role, regulation, and modulation by environmental pharmaceuticals

A series of experiments in this thesis confirm that ovarian synthesis of prostaglandins (PG) is necessary for normal ovulation in the zebrafish, Danio rerio. Initial studies demonstrated reduced egg production by fish exposed to the PG-synthesis inhibitor, indomethacin. Subsequent studies showed that ovarian levels of the maturation inducing steroid 17alpha,20beta-dihydroxy-4-pregnen-3-one (17alpha,20beta-P) rise during oocyte maturation and PGF2alpha , rise near the time of ovulation and spawning. Peak levels of cytosolic phospholipase A2 (cPLA2) and cyclooxygenase-2 (COX-2) gene expression in follicles are observed just prior to ovulation. Collectively, these findings led to the hypothesis that gonadotropin and 17alpha,20beta-P induce ovulation in zebrafish through the activation of the arachidonic acid pathway and the subsequent rise in PG levels results in expulsion of the oocyte. Both cPLA2 and COX-2 expression was increased in the ovaries of fish exposed in vivo to human chorionic gonadotropin or 17alpha,20beta-P, which supports the hypothesis.;Recently, pharmaceuticals have been detected in the aquatic environment and there is concern that they may impact fish reproduction. My studies with zebrafish have shown reduced egg production in fish exposed to high concentrations of diclofenac (a non-steroidal anti-inflammatory drug; NSAID), fluoxetine (FLU; a selective serotonin reuptake inhibitor), ethinylestradiol (EE 2, a synthetic estrogen), and municipal effluent, but the underlying biochemical or molecular mechanisms differed. These studies showed that FLU decreased ovarian estradiol levels and the expression of aromatase and gonadotropin receptors (FSHr, LHr) in the ovary. EE2 exerted its effects on steroid biosynthesis whereas the NSAID affected PG synthesis. High levels of ammonia/nitrite confounded the results from the municipal effluent study because of dissimilarities in water quality among the treatments. Municipal effluent and FLU induced the expression of detoxification genes in the liver (CYP3A65) whereas EE2 reduced the expression of CYP1A1 and CYP3A65. Provided that sufficient treatment replication is included, the short-term exposure regime used in these toxicity studies is suitable for studying the potential reproductive effects of environmental pharmaceuticals in zebrafish.